Offsets are points whose positions are specified by an offset distance and direction from another point. The offset distance displayed in the Traverse View is negative (-) for left offsets and positive (+) for right offsets.
The offset direction is dependent on the configuration of the point being offset.
TPC has an automatic setback tool
TPC makes it easy to compute offsets through the use of traverses.
You can determine how the offset points created will be labeled.
The offset tolerance determines how close the first and last point being offset need to be in order to be treated like a closed loop. If they do not reference the same survey point but are within the specified tolerance of each other, they will be considered the same point. The figure will close and you will get a single offset instead of two, as shown below.
If the figure you are offsetting is a closed loop, the first and last points are considered to be the same point, so the offset bisects the angle at that point. If they are not considered the same point, each one will have its own perpendicular offset.
As TPC computes the offsets, you can save these points one of two ways as 1) offsets (like sideshots) from their original points or 2) in a new traverse.
If you choose Save as Offsets, TPC creates an offset point from each point being offset in the current traverse. Offset points get drawn with the side shot settings in Drawing View. You can think of an offset point like a side shot from the point being offset.
If you choose Save as Traverse, TPC creates separate traverses for the left and right points. The created traverse name starts with Left dist followed by the original traverse name for the left offset and Right dist followed by the original traverse name for the right traverse.
Saving the offsets as a traverse creates a figure or boundary along the offset. You will use this option to show setbacks on a lot or right-of-ways along a centerline.
Starting in TPC Desktop 2011, TPC insures that this traverse receives a unique traverse name. It does this by appending a unique number to the traverse name. So for example, multiple offsets from the 'Centerline' traverse will be named 'Centerline1', 'Centerline2', etc.
For tangent-tangent offsets (where two tangents meet), TPC bisects the angle between the two tangenst to compute the resulting offset.
For sprial-tangent or curve-tangent offsets (where a spiral or curve meet a tangent), TPC does a series of computations that insure the computed offsets point meets the required offset from both the spiral/curve and the tangent.
Look at the diagram on the right.
As a result of this computation, the resuting direction from the radius point of the curve to the computed offset (blue radius) may not exactly match the direction from the radius point to the end point of the spiral/curve (red radius).
For curve-curve offsets, TPC does a Distance-Distance intersect using their two radius points and corresponding radii + offsets.
For offsets involving spirals, TPC relies on the Spiral Offset method you have selected from the Spiral Definitions you select in the Survey Definitions.
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